Replacing an adhesive pump (piston pump or gear pump) on a hot melt unit is a precise and potentially hazardous task due to the combination of high temperatures, high pressure and electricity.
Below is a general step-by-step plan. Please note: the exact procedure varies per brand (e.g. Nordson, Robatech, Melton, ITW Dynatec), but the basic principles remain the same.
⚠️ Safety warning: Hot melt adhesive can reach temperatures of up to 200°C. This causes severe burns. In addition, the system is often under high hydraulic pressure (up to 100 bar). Wear always heat-resistant gloves, safety goggles and protective clothing.
The most urgent advice: have this carried out by an experienced hot melt maintenance engineer! Hot melt service is available 24/7! The adhesive pressure is many times higher than the air pressure, and often, after removing the compressed air pressure on the pump, there is still a high residual hydraulic pressure in the system!
1. Preparation & Safety
Ensure you have the following tools and parts ready before you begin:
- New adhesive pump + new O-rings/seals (Never reuse old O-rings).
- Heat-resistant grease (e.g. Never-Seez or special O-ring grease).
- Torque wrench (crucial for correct assembly).
- Heat-resistant gloves and face protection.
- Cloths and cleaning agent (if necessary).
2. Securing the System
- Release pressure (Crucial): Even when the machine is switched off, there may still be hydraulic pressure in the system. Open the drain valve or activate the gun manually (if safe) to release the pressure to 0 bar to bring.
- Lowering the temperature: It is often easier to dismantle the pump when the adhesive is soft, but not red-hot. Allow the unit to cool to a safer temperature (e.g. around 60°C – 80°C), unless the manual specifies otherwise. Once the adhesive has completely cooled and hardened, it is often impossible to remove the pump without causing damage.
- Power off: Switch off the main switch and secure it (Lockout-Tagout) so that no one can switch on the machine during the changeover.
3. Dismantling the Old Pump
- Disconnect connections:
- Disconnect the electrical connections (if the pump is electrically heated or controlled).
- On a piston pump, disconnect the compressed air line (the pump is often pneumatically driven).
- Remove the bolts: Loosen the fixing bolts on the pump. Do this crosswise and carefully.
- Removing the pump: Pull the pump straight out of the manifold (the distribution block).
- Please note: Liquid adhesive may still come out. Have a cloth or container ready.
- Ensure that no old O-rings or debris remain in the hole.
4. Cleaning and Installation
The success of the replacement depends entirely on the cleaning.
- Inspection: Check the seat (the hole where the pump goes in) in the manifold. Are there any scratches or damage?
- Cleaning: Remove all burnt adhesive residue (char) from the seat. The surface must be perfectly clean to prevent leakage.
- Fitting O-rings:
- Lightly grease the new O-rings with the specified O-ring grease (heat-resistant).
- Place the O-rings on the new pump. Ensure that they are not twisted.
- Installing the pump: Carefully push the new pump straight into the manifold. Do not force it; if it is difficult to insert, check that the O-ring is not pinched.
5. Assembling and tightening
- Inserting bolts: First, tighten the bolts by hand.
- Torque: Use the torque wrench to tighten the bolts to the value specified in the manufacturer's manual.
- Tip: Turn them crosswise to distribute the tension evenly.
- Warning: Over-tightening may deform the manifold or break the bolts when they expand due to heat.
6. Start-up and Testing
- Warm up: Switch on the machine and allow it to warm up to operating temperature.
- Check: When the metal is hot, the materials expand. Check (carefully!) whether the bolts are still tight enough (hot-tightening), if the manufacturer recommends this.
- Building pressure: Slowly apply pressure to the system. Start with low air pressure.
- Leak check: Visually inspect for leaks around the pump flange.
- Function test: Test whether the pump strokes smoothly (in the case of a piston pump) or runs steadily (in the case of a gear pump) and whether the adhesive output is constant.
Hotmeltservice has various new original and reconditioned glue pumps in stock!
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